1. Field of the Invention
This invention relates generally to magnetic recording disks, including patterned-media disks wherein each data bit is stored in a magnetically isolated data island on the disk, and more particularly to a disk and disk drive with patterned phase-type servo patterns for head-positioning.
2. Description of the Related Art
Conventional magnetic recording disk drives use disks with “continuous” media, meaning that the magnetic recording layer is a continuous film of magnetizable material. In conventional continuous-media disks the concentric data tracks are not physically separated from one another and are not pre-formed in the recording layer, but are formed when the write fields from the write head create the magnetizations in the continuous magnetic layer. A continuous-media disk may also be a “discrete-track” disk, meaning that the concentric data tracks of continuous magnetic material are radially separated from one another by concentric nonmagnetic guard bands.
Magnetic recording hard disk drives with patterned magnetic recording media have been proposed to increase the data density. In patterned media, the magnetic recording layer on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional continuous media wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. Alternatively, the patterned media may be fabricated so that that there is no magnetic material in the spaces between the islands.
Like conventional non-patterned or continuous-media disks and discrete-track disks, patterned-media disks also have nondata servo regions that are used for read/write head positioning. The nondata servo regions in patterned-media disks contain patterned discrete servo blocks or islands separated by nonmagnetic spaces. The servo islands form a servo pattern that generates a servo readback signal that is demodulated into a position error signal (PES) for positioning the read/write head to the desired data track and maintaining it on track. The proposed method for formatting this type of disk is to DC “erase” the disk during manufacturing with a large magnet, leaving all of the servo islands magnetized in the same direction. Thus for a perpendicular magnetic recording disk, all of the servo islands would have a magnetization direction either “into” or “out of” the surface of the disk.
In patterned media, the data sectors as well as the nondata servo regions are patterned. However, it is also possible to fabricate a continuous-media disk wherein just the nondata servo regions are patterned. This type of continuous-media disk may have either conventional concentric data tracks, or discrete data tracks separated by nonmagnetic guard bands, but the nondata servo regions are patterned. An example of a discrete-track disk with patterned servo regions is described in U.S. Pat. No. 4,912,585.
One type of servo pattern is a phase-type servo pattern with PES fields that form “chevron” patterns. A chevron pattern is a first set of circumferentially-spaced servo islands inclined relative to the data tracks and a second set of servo islands that is the mirror image of the first set and circumferentially spaced from the first set about a generally radial line of symmetry. As the two sets of servo islands in the chevron pattern pass the read head, two sinusoidal readback signals are generated and the phase difference between the two sinusoidal signals is demodulated into the radial position of the read head relative to the nearest track centerline. However, this type of conventional phase-type servo pattern still requires a separate track identification (TID) field, typically a Gray-coded pattern, that must be read and decoded to determine the absolute position of the read head.
What is needed is a magnetic recording disk and disk drive with a chevron servo pattern of discrete patterned servo islands that can be demodulated to determine the absolute position of the read head without the need for a separate TID field.